Stent grafts for the thoracic aorta

ABSTRACT

A method of temporarily reducing the diameter of a stent graft ( 10 ) and a stent graft with its diameter reduced. The stent graft has a tubular body and self expanding stents. The method comprising extending a release wire ( 18, 20 ) part helically along the graft material tube from substantially one side of the graft material tube at one end ( 14 ) of the graft material tube to substantially the opposite side of the graft material tube at the other end ( 12 ) of the graft material tube along the stent graft and stitching the release wire into the graft material tube, at each of a number of positions along the release wire looping flexible threads ( 22, 24 ) around the release wire and extending the flexible threads laterally around the circumference of the stent graft in each direction to a position away from the release wire, engaging the first flexible threads into the graft material or around struts of the stent, and drawing the ends of the thread together and tying ends of the thread to thereby temporarily reduce the overall diameter of the stent graft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of provisional application Ser. No.60/928,731, filed May 11, 2007.

TECHNICAL FIELD

This invention relates to a medical device and more particularly to astent graft for mounting onto a deployment device for endovascularintroduction.

BACKGROUND OF THE INVENTION

This invention will be particularly discussed in relation to stentgrafts for placement into the thoracoabdominal aorta for the treatmentof aneurysms and more specifically in relation to placement in a curvedportion of the aorta such as the thoracic arch. The invention, however,is not so restricted and may be applied to stent grafts for placement inany lumen of the human or animal body.

A stent graft particularly for the thoracic arch may have one or morefenestrations or a scallop at the proximal end to prevent occlusion ofone or more of the major arteries which extend from the thoracic arch. Astent graft is in a constricted form when it is delivered by endoluminaltechniques to a deployment site within such a curved lumen and in thatcondition it is difficult for a physician to determine whether thefenestrations or scallop are correctly aligned to be positioned uponrelease by withdrawal of a covering sheath. There have been deviseddiameter reducing arrangements for stent grafts so that there is apartial release stage of the stent graft after the covering sheath hasbeen withdrawn. At this stage the stent graft has expanded in diameterto such an extent that the physician can visualise using radiographictechniques the position of the fenestrations or scallop while at thesame time the stent graft can still be rotated and move longitudinallyto position the fenestrations or scallop correctly. The diameterreducing arrangements can be subsequently released to allow the stentgraft to fully expand engage the wall of the vessel to form analternative flow path through the vessel to bypass an aneurysm, forinstance.

The problem with a curved lumen with significant continuing blood flowand such a staged release arrangement is that the proximal or leadingedge of the stent graft particularly at the inner side of the curvedlumen may not engage against the wall of the lumen and may fold inthereby blocking the desired flow path and allowing bypass to continueinto the aneurysm.

It is an object of this invention to provide a diameter reducingarrangement so that this problem can be reduced or to at least toprovide a physician with an alternative arrangement.

Throughout this specification the term distal with respect to a portionof the aorta, a deployment device or a prosthesis means the end of theaorta, deployment device or prosthesis further away in the direction ofblood flow away from the heart and the term proximal means the portionof the aorta, deployment device or end of the prosthesis nearer to theheart. When applied to other vessels similar terms such as caudal andcranial should be understood.

SUMMARY OF THE INVENTION

In one form therefore the invention is said to reside in a temporarydiameter reduction constraint arrangement for a stent graft, the stentgraft comprising a biocompatible graft material tube of a selecteddiameter and having a first end and a second end and a plurality of selfexpanding stents fastened thereto, the constraint arrangement comprisingat least one release wire extending part helically along the graftmaterial tube from substantially one side of the graft material tube atthe first end of the graft material tube to substantially the oppositeside of the graft material tube at the second end of the graft materialtube and a plurality of circumferential threads spaced apart atpositions along the graft material tube and engaged around the releasewire and a portion of the stent graft circumferentially spaced aselected distance away from the release wire and drawn tight and tied toreduce the circumference and hence the overall diameter of the stentgraft.

The stent graft can be mounted onto a deployment device such that at theproximal end of the stent graft the diameter reducing ties are at theinner side of what would be the curve of the deployment device to fitthe curved lumen and at the distal end they are on the outer side of thecurved lumen. This has a number of advantages. A first is that uponpartial release the outer side of the curve at the proximal end expandsmore fully while at the same time still being maneuverable which allowsthe fenestration or scallops to be more opened and hence easier tovisualise and position correctly. A second advantage is that when thediameter reducing ties are released by withdrawing the release wirethere is a certain degree of friction between the release wire and thegraft material through which it is stitched and pulling the release wireactually pulls the inner curve side of the proximal end of the stentgraft towards the inner curve of the lumen thereby assisting the innercurve side of the proximal end of the stent graft to correctly engagewith the wall of the lumen. A third advantage is that when the stentgraft is in its curved and partially released configuration the releasewire is substantially straighter between the ends of the graft therebyreducing the chance that the release wire will buckle and be difficultto withdraw when required.

Preferably the circumferential thread extends circumferentially in eachdirection from the release wire at each of the positions.

In a preferred embodiment the stents are zig-zag stents comprisingstruts and bends therebetween and the engagement of the flexible threadinto the graft material includes the engagement of the thread around astrut of the self expanding stent.

The selected distance may be reduced by from 50 to 75%.

In a preferred embodiment there may be two release wires and acircumferential thread extending circumferentially in each directionfrom each of the release wires at the plurality of positions along therelease wires to hold the stent graft at a reduced diameter along thelength of the stent graft. The two release wires may extend fromsubstantially the corresponding circumferential position at one end ofthe stent graft helically in opposite directions to substantially thecorresponding circumferential position at the other end of the stentgraft.

In an alternative form the invention comprises a method of temporarilyreducing the diameter of a stent graft at a plurality of positions alongthe stent graft, the stent graft comprising a tubular body of abiocompatible graft material and having a first end and a second end anda plurality of self expanding stents, the method comprising the stepsof;

a) extending a release wire part helically along the graft material tubefrom substantially one side of the graft material tube at the first endof the graft material tube to substantially the opposite side of thegraft material tube at the second end of the graft material tube alongthe stent graft and stitching the release wire into the graft materialtube;

b) at each of a plurality of positions along the release wire looping afirst flexible thread around the release wire and extending the firstflexible thread laterally around the circumference of the stent graft toa position a selected distance from the release wire;

c) engaging the first flexible thread into the graft material and/or astent strut, and

d) drawing the ends of the thread together and tying ends of the thread,

whereby the selected distance is reduced thereby temporarily reducingthe overall diameter of the stent graft.

The method can further comprise the steps of;

e) passing a second flexible thread around the release wire or the firstflexible thread and extending the second flexible thread laterallyaround the circumference of the stent graft in the opposite direction tothe first flexible thread to a position a selected distance from therelease wire at each of the plurality positions along the length of therelease wire;

f) engaging the second flexible thread into the graft material and/or astent strut, and

g) drawing the ends of the second thread together and tying ends of thethread,

whereby the selected distance is reduced thereby reducing the overalldiameter of the stent graft.

The method can further comprise the steps of;

j) extending a second release wire along the stent graft on an oppositeside of the graft material tube from substantially one side of the graftmaterial tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube along the stent graft and stitching therelease wire into the graft material tube;

k) looping a third flexible thread around the second release wire andextending the third flexible thread laterally around the circumferenceof the stent graft to a position a selected distance from the secondrelease wire;

l) engaging the third flexible thread into the graft material and/or astent strut, and

m) drawing the ends of the thread together and tying ends of the thread,

n) passing a fourth flexible thread around the release wire or aroundthe third flexible thread and extending the fourth flexible threadlaterally around the circumference of the stent graft in the oppositedirection to the third flexible thread to a position a selected distancefrom the second release wire;

o) engaging the fourth flexible thread into the graft material and/or astent strut, and

p) drawing the ends of the fourth thread together and tying ends of thethread,

whereby the selected distance is reduced thereby reducing the overalldiameter of the stent graft.

In an alternative form the invention comprises a temporary diameterreduction and constraint arrangement for a stent graft, the stent graftcomprising a biocompatible graft material tube of a selected diameterand a plurality of self expanding stents fastened thereto, the stentscomprising zig-zag stents comprising struts and bends therebetween, thetemporary diameter reduction and constraint arrangement comprising tworelease wires extending longitudinally and helically in oppositedirections along the graft material tube from substantially one side ofthe graft material tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube, the release wires being stitched intothe graft material tube, at a plurality of positions along each releasewire two threads engaged around each release wire and a selected strutof a stent and portion of the stent graft circumferentially spaced aselected distance away from each release wire in each circumferentialdirection from the respective release wires and drawn tight to compressthe self expanding stent between the selected strut and the release wireand tied to reduce the circumference and hence the overall diameter ofthe stent graft.

BRIEF DESCRIPTION OF THE DRAWING

This then generally describes the invention but to assist withunderstanding reference will now be made to drawings which showpreferred embodiments of the invention.

In the drawings:

FIG. 1A shows a schematic view of a stent graft with a helical diameterreducing tie arrangement and stylised cross sectional views at variousstages along the length of the stent graft according to one embodimentof the present invention;

FIGS. 1B to 1F show schematic cross sections along the length of thestent graft shown in FIG. 1A;

FIG. 2 shows a schematic view of the stent graft of FIG. 1 with thestent graft curved as it would be upon partial release within a curvedlumen of the body;

FIG. 3 shows a schematic view of the thoracic arch of the aorta of apatient with an aneurysm and with a stent graft at the partiallyreleased stage positioned in the aorta;

FIG. 4 shows the view of FIG. 3 with the diameter reducing tieswithdrawn and the stent graft expanded to the walls of the thoracicarch;

FIGS. 5A and 5B show detail of a diameter reducing arrangement usefulfor the present invention; and

FIG. 6 shows a schematic view of a stent graft with a diagonal orhelical diameter reducing tie arrangement mounted onto a delivery deviceand including a proximal retention arrangement according to analternative embodiment of the present invention.

DETAILED DESCRIPTION

Now looking more closely at the drawings and in particular FIGS. 1A to Fand FIG. 2 it will be seen that a stent graft 10 is a tubular body of asuitable graft material and has a proximal end 12 and a distal end 14. Ascallop 13 is provided in the stent graft at the proximal end 12. Thescallop would allow the stent graft to be deployed further around thethoracic arch of a patient thereby providing a larger landing zone forthe stent graft without occluding the left subclavian artery. Stents onthe stent graft are omitted in FIGS. 1 and 2 for the sake of clarity.

The stent graft is schematically depicted in a diameter reduced state bythe use of a diameter reducing arrangement generally shown as 16. Thediameter reducing arrangement includes release wires 18 and 20 whichextend down each side of the stent graft in a part helical manner inopposite directions from the distal end 14 to the proximal end 12. Therelease wire 18 is stitched in and out of the graft material along thelength of the stent graft to maintain it in position. The release wire20 is in a similar configuration on the other side of the stent graft.At intervals along the length of the stent graft threads 22 and 24 arelooped around the release wire and extended in opposite circumferentialdirections as will be discussed in detail with reference to FIGS. 5A and5B to hold the stent graft in a partially diameter reduced state. Thediameter reducing arrangements on each side therefore extend in a parthelical manner from one end of the stent graft to the other.

The cross sectional views FIGS. 1B to 1F at various stages along thelength of the stent graft shown in FIG. 1A illustrate in a stylisedmanner how the diameter reducing ties 22, 24 progress circumferentiallyaround the sides of the stent graft from one end to the other and aretied to the release wires 18 and 20.

At the proximal end of the stent graft 12 as shown in FIG. 1B theregions of diameter reduction 16 a and 16 b are close to each other atone side of the stent graft. At the distal end of the stent 14 as shownin FIG. 1F the regions of diameter reduction 16 c and 16 d are close toeach other at the other side of the stent graft. Between the proximaland distal ends as shown progressively in FIGS. 1C, 1D and 1E theregions of diameter reduction regions are positioned progressively upeach side of the stent graft.

FIG. 2 shows a schematic view of the stent graft 10 of FIG. 1 with thestent graft curved as it would be upon partial release within a curvedlumen of the body. The deployment device upon which the stent graft iscarried is not shown for purposes of clarity. When the release wires 18and 20 are pulled to release the diameter reducing ties 22 and 24 thenthe friction between the release wires and the threads and the graftmaterial will cause the inner curved side 15 of the end 12 to be pulledin a direction shown by the arrow 26 thereby encouraging the innercurved side 15 of the end 12 to correctly engage against the wall of alumen as it is released from it's temporary diameter constraint.

FIG. 3 shows a schematic view of the thoracic arch of the aorta of apatient with an aneurysm and with a stent graft at the partiallyreleased stage positioned in the aorta and FIG. 4 shows the view of FIG.3 with the diameter reducing ties withdrawn and the stent graft expandedto the walls of the thoracic arch.

The thoracic arch portion of the aorta comprises an ascending aorta 30which receives blood from the heart (not shown) though an aortic valve32. At the upper end of the ascending aorta there are branches for theinnominate artery 33, the left common carotid artery 34 and the leftsubclavian artery 35.

The aorta after these is referred to as the descending aorta 36 and itis in this region that an aortic aneurysm can occur. In an aorticaneurysm the wall of the aorta expands out to form a bulge 38 to leavean aneurysmal sac 39 which in serious cases can rupture with potentiallyfatal consequences. The aim of endovascular deployment of a stent graftis to isolate the aneurysmal sac by bypassing it with a stent graft. Animportant feature of placement of a stent graft in this region is thatthere is enough landing zone in the region 37 adjacent to the leftsubclavian artery 35 for the proximal end of the stent graft toadequately seal against a non-aneurysed portion of the thoracic arch. Toensure a sufficient landing zone the stent graft 10 can be provided witha scallop 13 which, when the stent graft is deployed will allowplacement of the stent graft further up in the thoracic arch withoutocclusion of the subclavian artery 35.

As can be seen in FIG. 3 the stent graft has been introduced on adeployment device 42 and at the stage shown in FIG. 3 the sheath 44 hasbeen withdrawn so that the stent graft 10 has partially expanded. Atthis stage the stent graft can still be moved on the introduction deviceto its desired position. The temporary diameter reducing arrangement 16on the stent graft 10 extends from the outside of the curve 46 at thedistal end 14 of the stent graft to the inside of the curve 48 at theproximal end 12 of the stent graft.

When the release wires 18 and 20 are retracted the stent graft expandsto the wall of the vessel as is shown in FIG. 4. It will be noted thatthe diameter reducing threads 22 and 24 remain in the graft afterremoval of the release wires but as they are on the outside of the stentgraft they do not occlude blood flow through the graft or provide pointsfor formation of thromboses.

By having the diameter reducing ties in the part helical configurationfrom one end of the stent graft to the other there are a number ofadvantages. A first is that upon partial release the outer side of thecurve at the proximal end expands more fully while at the same timestill being maneuverable which allows the scallop 13 to be more openedand hence easier to visualise and position correctly. A second advantageis that when the diameter reducing ties are released by withdrawing therelease wire they actually pull the inner curve side 15 of the proximalend 12 towards the inner curve of the lumen 48 thereby assisting theinner side of the proximal end of the stent graft 10 to correctly engagewith the wall of the lumen. A further advantage is that when the stentgraft 10 is in its curved and partially released configuration as shownin FIG. 3 the release wires 18 and 20 of the diameter reducingarrangement are substantially straighter between the ends 14 and 12 ofthe stent graft thereby reducing the chance that the release wire willbuckle and be difficult to withdraw when required. At the distal end ofthe stent graft the delivery device tends to be positioned at theoutside of the curve of the stent graft. The region at the distal endwhere the release wires 18 and 20 exit the stent graft is also on theoutside of the curve of the stent graft and hence the wires can easilyenter the delivery device 42 again reducing the chance that the releasewire will buckle and be difficult to withdraw when required.

FIGS. 5A and 5B show schematically one embodiment of diameter reducingtie arrangement useful for the present invention. In this drawing only aportion of the graft material of a stent graft is shown and only aportion of a self expanding stent is shown fastened to it and stretchedout flat.

As can be seen in FIG. 5A, a self expanding stent 70 which would extendaround the tubular body of a stent graft and be stitched by stitches 75to the graft material 72 of the stent graft is shown. A release wire 18is stitched longitudinally along the graft material of the stent graftas was seen in FIG. 1 with a stitch 18 a of the release wire beingexposed to the outside of the stent graft in the region of the selfexpanding stent 70.

A first suture thread 22 of a flexible material is passed around therelease wire 18 and extended out to one side of the release wire overthe struts 76 of the stent graft to pass over two or three struts and tobe looped around a third or fourth strut and into the graft material 72.The suture thread 22 is then pulled tight and knotted as shown in FIG.5B with a knot 78 so that the struts between the release wire 18 and theknot 78 are pulled closer together against the resilient force of theself expanding stent 70.

A similar action is carried out to the other side of the release wirewith a second suture thread 24 of a flexible material. In this case thethread 24 can either pass around the release wire 18 or be passedunderneath the two strands of the thread 22 and over the release wire 18and then it can be passed over two or three struts and then loopedaround a third or fourth strut and into the graft material 72 and pulledtight and knotted at 82.

The reduction in distance between the release wire 18 and the knot 78may be from 50 to 75 percent. For instance if the distance x in FIG. 5Ais 15 millimetres around the circumference of the stent graft from therelease wire 18 to the strut at which the knot 78 is placed then thiscan be reduced to 5 millimetres as shown by the dimension y in FIG. 5B.With two diameter reducing ties, one to each side of the release wire72, therefore a total circumference reduction of 20 millimetres can beachieved which will change the diameter of a 36 millimetre stent graftto approximately 28 millimetres. This can be less than the diameter ofthe aorta in that region into which the stent graft is deployed whichmeans that the stent graft will still be maneuverable within the aortawhile still mounted onto the deployment device but partially freed bythe withdrawal of a containing sheath.

FIG. 6 shows a schematic view of a stent graft with a diagonal orhelical diameter reducing tie arrangement mounted onto a delivery deviceand including a proximal retention arrangement according to analternative embodiment of the present invention. The embodiment issimilar to that shown in FIG. 1 and the same reference numerals are usedfor corresponding items.

In FIG. 6 it can be seen that a stent graft 10 has a proximal end 12 anda distal end 14. A scallop 13 is provided in the stent graft at theproximal end 12. The scallop would allow the stent graft to be deployedfurther around the thoracic arch of a patient to fit around the leftsubclavian artery, for instance, thereby providing a larger landing zonefor the stent graft without occluding the left subclavian artery. Stent17 on the stent graft is of the zig-zag or Z stent type and is showndotted in FIG. 6 for the sake of clarity.

The stent graft is schematically depicted in a diameter reduced state bythe use of a diameter reducing arrangement generally shown as 16. Thediameter reducing arrangement includes release wires 18 extending downeach side of the stent graft in a helical manner in opposite directionsfrom a distal end 14 to the proximal end 12. The release wire 18 isstitched in and out of the graft material of the stent graft to maintainit in position. A further release wire is in a similar configuration onthe other side of the stent graft. At intervals along the length of thestent graft threads 22 and 24 are looped around the release wire andextended in opposite circumferential directions as discussed in detailwith reference to FIGS. 5A and 5B to hold the stent graft in a partiallydiameter reduced state. The diameter reducing arrangements on each sidetherefore extend in a part helical manner from one end of the stentgraft to the other.

The stent graft is retained onto a delivery device 42 at its proximalend 12 just distal of a nose cone dilator 50 on a guide wire catheter 52which passes through the stent graft 10. Retention is by fasteningstruts of the proximal most stent to a trigger wire (not shown) by meansof a suture 54 as is explained in PCT Patent Publication WO 03/101518entitled “Trigger Wire System for a Prosthesis Deployment Device” theteaching of which is incorporated herein in its entirety.

In this embodiment the diameter reducing ties at the proximal end 12 donot meet at the bottom of the graft but are positioned slightly up therespective sides of the graft and the distal end is held up to the guidewire catheter by the retention arrangement such that the proximal end ofthe stent graft is of a size which enables it to be positioned in theascending aorta or the thoracic arch as necessary before final release.

Throughout this specification various indications have been given as tothe scope of the invention but the invention is not limited to any oneof these but may reside in two or more of these combined together. Theexamples are given for illustration only and not for limitation.

1. A temporary diameter reduction constraint arrangement for a stentgraft, the stent graft comprising a biocompatible graft material tube ofa selected diameter and having a first end and a second end and aplurality of self expanding stents fastened thereto, the constraintarrangement comprising at least one release wire extending parthelically along the graft material tube from substantially one side ofthe graft material tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube and a plurality of circumferentialthreads spaced apart at positions along the graft material tube andengaged around the release wire and a portion of the stent graftcircumferentially spaced a selected distance away from the release wireand drawn tight and tied to reduce the circumference and hence theoverall diameter of the stent graft.
 2. A constraint arrangement as inclaim 1 wherein the circumferential thread extends circumferentially ineach direction from the release wire at each of the positions.
 3. Aconstraint arrangement as in claim 1 wherein the stents are zig-zagstents comprising struts and bends therebetween and the engagement ofthe flexible thread into the graft material includes the engagement ofthe thread around a strut of the self expanding stent.
 4. A constraintarrangement as in claim 1 wherein the selected distance is reduced byfrom 50 to 75%.
 5. A constraint arrangement as in claim 1 comprising tworelease wires and a circumferential thread extending circumferentiallyin each direction from each of the release wires at the plurality ofpositions along the release wires to hold the stent graft at a reduceddiameter of the stent graft along the length of the stent graft.
 6. Amethod of temporarily reducing the diameter of a stent graft at aplurality of positions along the stent graft, the stent graft comprisinga tubular body of a biocompatible graft material and having a first endand a second end and a plurality of self expanding stents, the methodcomprising the steps of; a) extending a release wire part helicallyalong the graft material tube from substantially one side of the graftmaterial tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube along the stent graft and stitching therelease wire into the graft material tube; b) at each of a plurality ofpositions along the release wire looping a first flexible thread aroundthe release wire and extending the first flexible thread laterallyaround the circumference of the stent graft to a position a selecteddistance from the release wire; c) engaging the first flexible threadinto the graft material, and d) drawing the ends of the thread togetherand tying ends of the thread, whereby the selected distance is reducedthereby temporarily reducing the overall diameter of the stent graft. 7.A method as in claim 6 wherein the stents are zig-zag stents comprisingstruts and bends therebetween and the step of engaging the firstflexible thread into the graft material includes engaging the threadaround a strut of a self expanding stent.
 8. A method as in claim 6further comprising the steps of; e) passing a second flexible threadaround the release wire and extending the second flexible threadlaterally around the circumference of the stent graft in the oppositedirection to the first flexible thread to a position a selected distancefrom the release wire at each of the plurality positions along thelength of the release wire; f) engaging the second flexible thread intothe graft material, and g) drawing the ends of the second threadtogether and tying ends of the thread, whereby the selected distance isreduced thereby reducing the overall diameter of the stent graft.
 9. Amethod in claim 6 wherein the selected distance is reduced by from 50 to75%.
 10. A method as in claim 6 further comprising the steps of; j)extending a second release wire along the stent graft on an oppositeside of the graft material tube from substantially one side of the graftmaterial tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube along the stent graft and stitching therelease wire into the graft material tube; k) looping a third flexiblethread around the second release wire and extending the third flexiblethread laterally around the circumference of the stent graft to aposition a selected distance from the second release wire; l) engagingthe third flexible thread into the graft material, and m) drawing theends of the thread together and tying ends of the thread, n) passing afourth flexible thread around the release wire or around the third andextending the fourth flexible thread laterally around the circumferenceof the stent graft in the opposite direction to the third flexiblethread to a position a selected distance from the second release wire;o) engaging the fourth flexible thread into the graft material, and p)drawing the ends of the fourth thread together and tying ends of thethread, whereby the selected distance is reduced thereby reducing theoverall diameter of the stent graft.
 11. A temporary diameter reductionand constraint arrangement for a stent graft, the stent graft comprisinga biocompatible graft material tube of a selected diameter and aplurality of self expanding stents fastened thereto, the stentscomprising zig-zag stents comprising struts and bends therebetween, thetemporary diameter reduction and constraint arrangement comprising tworelease wires extending longitudinally and helically in oppositedirections along the graft material tube from substantially one side ofthe graft material tube at the first end of the graft material tube tosubstantially the opposite side of the graft material tube at the secondend of the graft material tube, the release wires being stitched intothe graft material tube, at a plurality of positions along each releasewire two threads engaged around each release wire and a selected strutof a stent and portion of the stent graft circumferentially spaced aselected distance away from each release wire in each circumferentialdirection from the respective release wires and drawn tight to compressthe self expanding stent between the selected strut and the release wireand tied to reduce the circumference and hence the overall diameter ofthe stent graft.